Heretofore, as an example for a coupling structure of an optical waveguide to a light-receiving device, the one shown in FIG. 1 is usual.
In the coupling structure, an optical waveguide 4 made of a quartz-base material and having a structure wherein a long core 2 having a high index of refraction and a square or rectangular section is enclosed with a cladding 3 having a low index of refraction is formed on a base 1 made of a silicon substrate or the like, an end plane 2a of the core 2 is opposed to a light-receiving plane 6 of a photodiode (PD: light-receiving device) 5, the end plane 2a of the core 2 is positioned in such that the center thereof coincides substantially with the center of the light-receiving plane 6 of the photodiode 5, and then, the photodiode 5 is fixed to on the base 1.
Since it is required to position the center of the end plane 2a of the core 2 in such that the former center coincides substantially with the center of the light-receiving plane 6 of the photodiode 5 in the above described structure, there is such a manner that markers (register marks) indicating positions of the optical waveguide 4 and the photodiode 5, respectively, have been previously prepared on the base 1, and the optical waveguide 4 and the photodiode 5 are fixed after having been in register, respectively, in the case where the optical waveguide 4 and the photodiode 5 are fixed on the base 1.
Meanwhile, since it is required to fix the optical waveguide 4 and the photodiode 5 on the base 1 made of a silicon substrate and the like in the above-mentioned conventional coupling structure of optical waveguide to light-receiving device, there have been a problem of requiring an extra material of the base 1, so that it is difficult to downsize the whole structure, and another problem of a difficulty t o lower costs for the structure, because the base 1 must be used in the structure so that it becomes expensive.
Furthermore, such a manner that markers for indicating positions of the optical waveguide 4 and the photodiode 5 have been previously formed on the base 1, respectively, and then, the optical waveguide 4 and the photodiode 5 are fixed so as to maintain register in the respective markers is applied in the above described structure. In this case, however, variations in positions of the respective markers formed on the base 1 are significant, and further variations in positioning of the optical waveguide 4 and the photodiode 5 in case of securing them on the markers thus formed are also remarkable. As a result, there is a problem of magnifying further relative positional displacements in the core 2 of the optical waveguide 4 with respect to the light-receiving plane 6 of the photodiode 5, resulting in defective products due to the positional discrepancies, in turn, it becomes a cause for reducing an yield of products.